Keratin treatment and Rogaine?

Technically speaking you can. The concern really centres around the use of the keratin as some types are well known to contribute to hair breakage -especially formaldehyde containing formulations. These tend to be more rare. Any heat can contribute to breakage so if the underlying hair loss condition a patient has is associated with increased fragility to begin with, then keratin could certainly worsen things. Underlying scalp issues like seborrheic dermatitis and psoriasis should be addressed before one gets keratin treatments.

Yes, the two modalities can work together. Keritin fibers in the from of a product called Toppik works for many people